73649dab0f
The following patch adds the x86_64 architecture specific implementation for function return probes. Function return probes is a mechanism built on top of kprobes that allows a caller to register a handler to be called when a given function exits. For example, to instrument the return path of sys_mkdir: static int sys_mkdir_exit(struct kretprobe_instance *i, struct pt_regs *regs) { printk("sys_mkdir exited\n"); return 0; } static struct kretprobe return_probe = { .handler = sys_mkdir_exit, }; <inside setup function> return_probe.kp.addr = (kprobe_opcode_t *) kallsyms_lookup_name("sys_mkdir"); if (register_kretprobe(&return_probe)) { printk(KERN_DEBUG "Unable to register return probe!\n"); /* do error path */ } <inside cleanup function> unregister_kretprobe(&return_probe); The way this works is that: * At system initialization time, kernel/kprobes.c installs a kprobe on a function called kretprobe_trampoline() that is implemented in the arch/x86_64/kernel/kprobes.c (More on this later) * When a return probe is registered using register_kretprobe(), kernel/kprobes.c will install a kprobe on the first instruction of the targeted function with the pre handler set to arch_prepare_kretprobe() which is implemented in arch/x86_64/kernel/kprobes.c. * arch_prepare_kretprobe() will prepare a kretprobe instance that stores: - nodes for hanging this instance in an empty or free list - a pointer to the return probe - the original return address - a pointer to the stack address With all this stowed away, arch_prepare_kretprobe() then sets the return address for the targeted function to a special trampoline function called kretprobe_trampoline() implemented in arch/x86_64/kernel/kprobes.c * The kprobe completes as normal, with control passing back to the target function that executes as normal, and eventually returns to our trampoline function. * Since a kprobe was installed on kretprobe_trampoline() during system initialization, control passes back to kprobes via the architecture specific function trampoline_probe_handler() which will lookup the instance in an hlist maintained by kernel/kprobes.c, and then call the handler function. * When trampoline_probe_handler() is done, the kprobes infrastructure single steps the original instruction (in this case just a top), and then calls trampoline_post_handler(). trampoline_post_handler() then looks up the instance again, puts the instance back on the free list, and then makes a long jump back to the original return instruction. So to recap, to instrument the exit path of a function this implementation will cause four interruptions: - A breakpoint at the very beginning of the function allowing us to switch out the return address - A single step interruption to execute the original instruction that we replaced with the break instruction (normal kprobe flow) - A breakpoint in the trampoline function where our instrumented function returned to - A single step interruption to execute the original instruction that we replaced with the break instruction (normal kprobe flow) Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> |
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.. | ||
acpi | ||
cpufreq | ||
aperture.c | ||
apic.c | ||
asm-offsets.c | ||
e820.c | ||
early_printk.c | ||
entry.S | ||
genapic_cluster.c | ||
genapic_flat.c | ||
genapic.c | ||
head64.c | ||
head.S | ||
i387.c | ||
i8259.c | ||
init_task.c | ||
io_apic.c | ||
ioport.c | ||
irq.c | ||
kprobes.c | ||
ldt.c | ||
Makefile | ||
mce_intel.c | ||
mce.c | ||
module.c | ||
mpparse.c | ||
msr.c | ||
nmi.c | ||
pci-dma.c | ||
pci-gart.c | ||
pci-nommu.c | ||
pmtimer.c | ||
process.c | ||
ptrace.c | ||
reboot.c | ||
semaphore.c | ||
setup64.c | ||
setup.c | ||
signal.c | ||
smp.c | ||
smpboot.c | ||
suspend_asm.S | ||
suspend.c | ||
sys_x86_64.c | ||
syscall.c | ||
time.c | ||
trampoline.S | ||
traps.c | ||
vmlinux.lds.S | ||
vsyscall.c | ||
x8664_ksyms.c |